Investigating the interface of NLRX1 and immune aging

Project Summary/Abstract: Alterations in the immune system occur with aging, likely contributing to infections and malignancies. In T cells, probably the most prominent change with aging is memory T cell expansion. A possible mechanism for this finding is immune stimulation over a lifetime. The nucleotide binding

domain and leucine-rich-repeat-containing (NLR) protein X1 or NLRX1 located in mitochondria is a negative regulator of multiple inflammatory pathways including the retinoic acid-inducible gene I (RIG-I), NLR pyrin domain containing 3 (NLRP3) inflammasome, and NF-κB signaling. Our published and preliminary studies

support the possible implication of NLRX1 in aging. Aging induced the reduction of NLRX1 in murine lungs. The lungs from whole body NLRX1 null mutant (-/-) or knockout (KO) mice revealed increased lung compliance, a key feature of the “aging lung”8. Of interest, we found decreased expression of NLRX1 in peripheral blood

mononuclear cells (PBMCs) of older adults, raising the implication of NLRX1 in immune aging. Indeed, the NLRX1 KO mice have changes in T cell immunity known to occur with aging. These changes include an expansion of memory CD4+ and CD8+ T cells, decreased naïve T cell survival and IL-2 production, increased T

cell exhaustion molecules and effector cytokine IFN-γ. Our RNA-seq analysis on effector memory (EM) CD4+ T cells of WT and NLRX1 KO mice highlighted an aging-like change in the global gene expression profile in NLRX1 KO mice, implying the role of NLRX1 in altering T cell immunity with aging. This point is further

supported by noticing well-known age-associated changes in NLRX1 KO mice, including reduced mitochondrial mass, nicotinamide adenine dinucleotide (NAD+) and SIRT1 as well as enhanced mitochondrial reactive oxygen species (ROS), mTOR activation, hypoxia-inducible factor 1-alpha (HIF-1α) expression and

cellular exhaustion which are mechanistically linked. However, our understanding remains poor about how NLRX1 plays in altering T cell immunity in the context of aging biology and whether such changes can be restored by increasing NLRX1 in aged hosts. Here we address this question based on the hypotheses that

decreased NLRX1 augments T cell aging by mechanistically affecting a set of aging-associated molecules (i.e., mitochondrial ROS, NAD+, SIRT1, and mTOR) and that such aging-associated changes can be improved by restoring NLRX1 expression in old mice. The goal of our proposal is to test these hypotheses with the following

specific aims: 1) Aim 1. Elucidate the mechanism of how NLRX1 deficiency alters T cell characteristics, especially ones related to immune aging; 2) Aim 2. Elucidate the implication of mitochondrial ROS and NAD+ in inducing T cell immunity changes via affecting mTOR activity in NLRX1 KO mice; and 3) Aim 3. Elucidate

whether restoration of NLRX1 in vivo can attenuate aging-associated changes in T cell immunity. The results of our study will reveal a novel mechanism of T cell aging in the setting of decreased NLRX1, providing a potential anti-aging strategy by restoring NLRX1.